setting size and flash top config

[tballmsft]

this PR has two major changes to allow more efficient use of flash memory

1. the ability to configure the size of the libs/settings extension via Static TypeScript (using getConfig)
2. communication of the top of usable flash from the CODAL/C++ toolchain to MakeCode (as under different compile options to C++, we may get different top of flash)

the second part puts the top of flash (FLASH_TOP from compile) into the PXT shim table

#define PXT_SHIMS_BEGIN                                                                            \
    namespace pxt {                                                                                \
    const uintptr_t functionsAndBytecode[]                                                         \
        __attribute__((aligned(0x20))) = {0x08010801, 0x42424242, 0x08010801, 0x8de9d83e, FLASH_TOP,

This requires changes to hexfile.ts to extract FLASH_TOP from the hex file (or ELF) produced by the C++ compiler tool chain

Related PRs:

• setting size config pxt-common-packages#1502
• add settings config pxt-microbit#6110

TODO:

• make sure this works also for pxt-arcade

[mmoskal]

LGTM!